11. Microbial Genetic I: Gene Structure, Replication, And Expression

Front 1

The Organization of DNA in Prokaryotic Cells: Archaea and Bacteria

Back 1

- DNA is a circular double helix

- further twisting results in supercoiled DNA

- supercoiling is required so that the chromosome "fits" into the cell

- in bacteria, the RNA is associated with protein HU

Front 2

DNA gyrase

Back 2

A topoisomerase creates supercoils to compact bacterial chromosome

Front 3

Protein HU

Back 3

Helps organize DNA into a packed chromatin linked structure

Front 4

DNA Replication in Prokaryotes

Back 4

- Replication begins at a "single" site known as the origin of replication

- multienzyme replication complex binds to origin

- separated DNA strands serve as templates for DNA polymerase

- 2 characteristic replication forks are formed, which proceed in opposite directions around the chromosome

- 2 copies of the total genetic information produced during replication are each composed of one parental strand and one newly synthesized strand of DNA (semi conservation replication)

Front 5

Semi Conservation Replication

Back 5

2 copies of the total genetic information produced during replication are each composed of one parental strand and one newly synthesized strand of DNA

Front 6

Origin of Replication

Back 6

"Single" site where replication starts

Front 7

Helicases

Back 7

Seperate and unwind DNA strands

Front 8

Topoisomerases

Back 8

Relieve tension generated by rapid unwinding (transiently break one or two strands without altering nucleotide sequence)

Front 9

Single-Stranded DNA binding proteins (SSBs)

Back 9

Keeps the strands apart once separated

Front 10

Chromosome Replication and Partitioning (3 Elements)

Back 10

In most prokaryotes:

Origin of replication: site at which replication begins

Terminus: site at which replication is terminated

Bidirectional from a single origin of replication

Front 11

DNA Replication in Rapidly Growing Cells: Cell Cycle

Back 11

Cell cycle completed in 20 minutes

40 minutes for DNA replication,

20 minutes for septum formation and cytokinesis

- Second, third, or fourth round of replication can begin before first round of replication is completed

- when bacteria are growing rapidly, they initiate new rounds of DNA replication before an existing round of replication has finished (daughter cells inherit DNA that has already initiated its own replication)

Front 12

Cell cycle completed in __ minutes: ___ minutes for DNA replication,

___ minutes for septum formation and cytokinesis. How is this possible?

Back 12

20, 40,20

Why? Second, third, or fourth round of replication can begin before first round of replication is completed

Front 13

DNA Polymerases

Back 13

Catalyze synthesis of complementary strand of DNA (DNA polymerase III plays major role in replication in prokaryotes)

- require template, primer, dNTPs

Front 14

DNA synthesis is in ___ and nucleotides are linked by ___ bonds

Back 14

5' to 3' direction; phosphodiester

Front 15

DNA Polymerases require __,__, and __.

Back 15

- Template: directs synthesis of complementary strand

- Primer: RNA strand to provide a 3' hydroxyl group to which nucleotides can be added; made by primase

- dNTPs (dATP, dTTP, dCTP, dGTP): deoxynucleoside triphosphates

Front 16

Leading Strand

Back 16

Synthesized continuously at its 3' end as the DNA unwinds as DNA polymerase enzymes must synthesize DNA in the 5' to 3' direction

Front 17

Lagging Strand

Back 17

- cannot be extended in the same direction because there is no free 3' OH to which a nucleotide can be added

- synthesized discontinuously in the 5' to 3' direction as a series of fragments

Front 18

Primase

Back 18

Adds many RNA primers along the single-stranded lagging strand

Front 19

DNA Polymerase III

Back 19

Extends primers made by primase with DNA to form short fragments

Front 20

Helicase

Back 20

Unwind DNA

Front 21

Topoisomerases

Back 21

Relieve tension generated by rapid unwinding

Front 22

DNA polymerase

Back 22

Catalyzed DNA synthesis

Front 23

Okazaki Fragments

Back 23

Lagging strand is synthesized in short fragments; a new primer is needed for the synthesis of each Okazaki fragment

Front 24

Completion of Lagging Strand Synthesis

Back 24

- DNA polymerase I removed the RNA primer and fills gap with DNA but a nick remains

- Okazaki fragments are joined by the enzyme DNA ligase; forms phosphodiester bond between 3' hydroxyl of the growing strand and the 5' phosphate of an Okazaki fragment

Front 25

DNA Polymerase III

Back 25

- does proofreading

- checks each newly incorporated base to see that it forms stable hydrogen bonds

Front 26

DNA Polymerase III

Back 26

- mismatched base removed from 3' end of growing strand by exonuclease activity of the DNA polymerase III enzyme; adds proper base after

Front 27

Termination site (ter in E.coli)

Back 27

Where replication stops when replisome reaches here

Front 28

Tus Proteins

Back 28

Binds to ter sites and halts progression of the forks

Front 29

Catenanes

Back 29

Form when 2 circular daughter chromosomes are interlocked following replication of the DNA and do not separate

Front 30

____ solves this problem of not seperation by temporarily breaking the DNA molecules so the strands can seperate

Back 30

Topisimerases